help!

okay so I'm 10 ( yes I know that's really young but please don't judge me) and I have been noticing some things. I've noticed that my stomach has been growing fast and whenever I put my hand on my stomach I feel a bumping like a heart beat. So you're probably wondering how I got a baby inside me if I did. So my brother and his girlfriend stayed in the room that is mine now and you know they probably did something. Anyway I haven't told my mom although I know I should. Please someone help me or tell me something informative.